Driven by the need to develop high electrical energy storage devices and miniaturisation of electronic devices down to the micro and/or nanometer scale; increasing attention has been concentrated on the development of high or giant dielectric constant materials with good thermal stability and low dielectric loss.
To date, there are few materials systems which have a dielectric constant above 104. Examples include BaTiO3-like perovskite relaxor ferroelectric materials, such as BaTi0.9(Ni, W)0.1O3, Ba(Fe0.5Ta0.5)O3, (Ba, Sr)TiO3, Ba(Ti, Sn)O3; CaCu3Ti4O12 (CCTO) as well as analogous compounds like CdCu3Ti4O12, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12 and Li (and/or K), and Ti (and/or V) co-doped NiO. In the first BaTiO3-like perovskite system, the giant dielectric constant (about 103-104) arises from their relaxor ferroelectric characteristics with a displacive diffuse transition in the vicinity of room temperature. The dielectric constant of materials of this type, however, is significantly temperature and frequency dependent with a relatively large dielectric loss. The giant dielectric constant of the second CCTO-type family of materials can reach up to about 105. These CCTO-type materials have relatively better temperature stability since the high dielectric polarisation results from both relaxor ferroelectric and internal barrier layer capacitance (IBLC) contributions. The dielectric properties of materials of this type, however, are often strongly process-dependent. For example, the measured dielectric constant can vary over the range from a few hundred up to 105. The doped NiO and La2-xSrxNiO4 (x=⅓ or ⅛) systems are ones where the dielectric constant arises from IBLC or so called core-shell model contributions. This, again, however leads to a relatively high dielectric loss over a relatively broad temperature range.
There is therefore a need for a material which exhibits a giant dielectric constant but better temperature stability and significantly less dielectric loss by comparison with existing giant dielectric constant materials.